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British doctors succesfully separated Sudanese twins who were joined at the top of their heads in a rare and risky operation that appears to have gone perfectly.

The four-stage procedure on 11-month-old Rital and Ritag Gaboura was funded by Facing the World, a charity which helps children from around the world. The girls' heads were cut apart and then each was sealed with tissue expanders in the surgeries, at London's Great Ormond Street Hospital. On Sunday, the smiling twins were displayed for news outlets, their heads still wrapped in bandages.

"Incidences of surviving twins with this condition is extremely rare," lead surgeon David Dunaway said in a statement released by the charity. "The task presented innumerable challenges and we were all very aware of our responsibilities to the family and these two little girls."

Twins born joined at the head are called craniopagus twins, and the condition occurs in about one in 2.5 million births, according to The Associated Press. Because conjoined twins don't pump blood evenly, the strongest sibling strains his or her heart trying to make up the difference. Ritag's heart was already failing by the time her family arrived in Britain.

The operation appears to have gone as well as could be hoped. "

Within days the twins were back on the general ward interacting and playing as before," the charity said. Its executive coordinator, Sarah Driver-Jowitt, predicted that the girls' parents — who haven't been named — may soon return home "with two healthy, separate girls."